The present invention relates to a temperature sensor of the type used in the automotive industry for measuring the temperature of the coolant fluid for an engine, and more particular such a sensor that has improved precision and reliability. The invention also relates to the method for producing such a sensor.
Temperature sensors for the coolant fluid for an engine are generally made up of a sensitive element, most often a thermistor, connected by flat pin connection terminals to an external electronic system. These flat pin connection terminals are held by a body of plastic material compound-filled around them to form a connector. From French Patent Application 2 719 115, a sensor of this type is known in which this compound-filling also includes the sensitive element and completely forms the sensor. When the sensor must be mounted in screwed fashion to the engine cylinder head, one may be led to compound-fill the body inside a metal cup that is partly or completely closed at its end that is in contact with the coolant liquid. When a closed cup is used, the heat transfer between the coolant liquid and the sensitive element is impaired by the interface between the metal of the cup and the plastic compound-filling material, as well as by this material itself, hence leading to a loss of precision and a poorer response time of the pickup. Furthermore, the rigidity of the cup and the compound-filling material and their different coefficients of expansion can lead to mechanical stresses on the sensitive element and its linkages with the flat pin connection terminals, thus causing breakdowns and impairing the reliability of the sensor.
It is accordingly the object of the present invention to overcome these disadvantages of the prior art. These objects of the invention, as well as others which will become apparent in the course of the present description, are attained by means of a temperature sensor, of the type including a body holding flat pin connection terminals connected to a sensitive element, which body is compound-filled in a cup, characterized in that the sensitive element is embedded in a thermal paste acting as a stop wall for the compound-filling material forming the body.
In an important characteristic of the present invention, the cup includes an anchoring groove of the compound-filling material forming the body.
The invention also relates to a method for producing a temperature sensor of this type, characterized in that, before the operation of compound-filling of the body, a thermal paste in a quantity sufficient to cover the sensitive element is placed at the bottom of the cup, which thermal paste serves a stop wall for the compound-filling material.
Further characteristics and advantages of the invention will become apparent from reading the ensuing description and studying the accompanying drawing, in which the sole FIGURE shows a sectional view of such a sensor.